Rule 3.17

Rule 3.17
Players and substitutes of both teams shall confine themselves to their team’s benches unless actually participating in the play or preparing to enter the game, or coaching at first or third base. No one except players, substitutes, managers, coaches, trainers and bat boys shall occupy a bench during a game.

PENALTY: For violation the umpire may, after warning, remove the offender from the field.
 
Rule 3.17 Comment: Players on the disabled list are permitted to participate in pre-game activity and sit on the bench during a game but may not take part in any activity during the game such as warming up a pitcher, bench-jockeying, etc. Disabled players are not allowed to enter the playing surface at any time or for any purpose during the game.


DISCUSSION
The only player to occupy the on-deck circle is the player next scheduled to bat. [MLBUM]


Rule 3.17 is strictly enforced by MLB Baseball.
Former Boston Red Sox player Johnny Pesky cannot sit on the Boston bench during MLB contests.
http://www.bostonglobe.com/sports/2007/03/30/baseball-rule-will-force-johnny-pesky-out-dugout/ueA55K0p8K2hOUGjPmXOmM/story.html

Players on the disabled list are confined to the dugout during the game and are not permitted to bench-jockey.

Player on the disabled list is ejected for arguing balls and strikes.

http://mlb.mlb.com/video/play.jsp?content_id=11723277

Disabled player acts as bat boy for the game.

http://mlb.mlb.com/video/play.jsp?content_id=11001059&c_id=mlb